62911 Free/Reward Site Backend

I'm looking for a backend system to serve a site similiar to [login to view URL] - basically we need a mechanism for user account creation and a mechanism which appends a userid of some sort to each user/offer link and then determines which users have completed an offer based upon data reported back via excel sheets. The script would then need to give a 'gift code' from a pre-compiled database/file of gift codes to the users who have completed offers, delete the used code from the database & avoid sending codes to users who have not yet completed offers. The system would need to be versatile enough to allow users to log-in at a later time to either complete a different offer for a second code OR retrieve/review codes that were already issued. A mutual non-disclosure agreement will be required upon project delegation.